1. Field of the Invention
The invention relates to an exhaust gas recirculation device of an internal combustion engine. More particularly, the invention relates to an exhaust gas recirculation device of an internal combustion engine which includes an exhaust gas recirculation (EGR) passage that links an exhaust passage and an intake passage of the internal combustion engine, an EGR valve that blocks the EGR passage when closed, and an EGR catalyst that purifies the exhaust gas flowing in the EGR passage, and which causes the exhaust gas flowing in the exhaust passage to recirculate to the intake passage.
2. Description of the Related Art
An exhaust gas recirculation device is known in which the exhaust gas is recirculated to an intake passage via an EGR passage linking an exhaust passage and an intake passage of an internal combustion engine. The so-called external EGR by which the exhaust gas is recirculated inside cylinders of an internal combustion engine via an EGR passage can improve fuel consumption.
An EGR catalyst that purifies the exhaust gas flowing in the EGR passage and the EGR valve that regulates the amount of exhaust gas flowing in the EGR passage are sometimes provided in the EGR passage, as in an exhaust recirculation system of an internal combustion engine disclosed in Japanese Patent Application Publication No. 2005-264821 (JP-A-2005-264821), in a device that thus recirculates the exhaust gas to the intake passage via the EGR passage.
For the EGR catalyst to provide a sufficient purification function, a warm-up state has to be assumed in which the EGR catalyst temperature is equal to or higher than a predetermined temperature. Therefore, it is desirable that a decrease in temperature of the EGR catalyst during operation of an internal combustion engine be inhibited and the warm-up state of the EGR catalyst be maintained. Inhibition of temperature decrease in the EGR catalyst during operation of an internal combustion engine has not been heretofore sufficiently investigated.
For example, when an EGR valve has been provided in the EGR passage, the EGR valve is not necessarily open at all times. There is a period in which the EGR valve is closed, the EGR passage is blocked, and the exhaust gas does not flow into the EGR passage, this period being determined based on operating conditions of the internal combustion engine or the like. When the exhaust gas thus does not flow to the EGR passage, the EGR catalyst temperature may drop and purification performance may be degraded.
Accordingly, it is desirable to enable the decrease in temperature of the EGR catalyst in an exhaust gas recirculation device of an internal combustion engine including an EGR passage linking an exhaust passage and an intake passage of the internal combustion engine, an EGR valve that blocks the EGR passage when closed, and an EGR catalyst that purifies an exhaust gas flowing in the EGR passage and performing exhaust gas recirculation control by which the EGR valve is opened and the exhaust gas flowing in the exhaust passage is recirculated to the intake passage via the EGR passage.